THE MEASUREMENT OF THYROID STIMULATING HORMONE (TSH) IN BODY FLUIDS: A CRITICAL REVIEW

Abstract

A large number of methods for estimation of thyrotrophin (TSH) have been proposed. The reliability criteria of some of these methods are reviewed and their applicability to clinical studies discussed. The chief difficulty in the clinical application of TSH assays lies in the lack of methods of sufficient sensitivity to detect the hormone in the very small quantities in which it is present in body fluids. Results of TSH assays should now be expressed in terms of the International Standard. Much of the confusion which exists in the literature arises from the use of various «animal units» and from the fact that results obtained in one centre cannot be compared with those in another. Techniques depending on radiometric criteria are generally sensitive, rapid and simple to perform. For these reasons they are probably the procedures of choice for clinical investigations. In euthyroid subjects TSH levels in blood are low and range from zero to 0.5 ImU/ml of serum. In patients with untreated myxocdema higher levels are generally found; these lie in the range 2.0 to 8.0 ImU/ml. In thyrotoxicosis, the TSH concentration in serum is variable but frequently found to be higher than that in euthyroid subjects; values quoted in the literature range from zero to 1.5 ImU/ml. No correlation has been demonstrated, in patients with exophthalmos, between the degree of exophthalmos and the level of circulating TSH. Future work in the field of TSH investigations will probably be concerned with the development of further in vitro assay methods and with the improvement of fractionation techniques by means of which concentrated extracts containing the hormone can be prepared from blood and urine.